Unhexoctium
Unhexoctium, also known as eka-oganesson or element 168, is the temporary name of a hypothetical superheavy chemical element in the periodic table that has the temporary symbol Uho and has the atomic number 168. In the periodic table of elements, it is a p-block element and the last one of the 8th period. As of 2012, no attempt has been made to synthesize this element. It is predicted to be a noble gasUnhexoctium - Elements Wiki, but according to the Pyykkö model, unhexoctium is predicted to be a post-transition metal right below unquadnilium. Nuclear Properties At least one set of theoretical values for half-lives and decay modes of Uho have been constructed for neutron count up to N = 333(5). It predicts isotopes in a band ranging from Uho 457 to Uho 484. Examination of pp 15 & 18 of Ref. 5 indicates that Uho 457 through Uho 460 are predicted to decay by fission and have sub-microsecond half-lives. Uho 461 to Uho 476 decay by alpha emission with half-lives increasing with A and peaking at 0.001 – 1 sec in the Uho 473 to Uho 476 range. Heavier isotopes also decay by alpha emission, but have short halflives. These predictions are to be expected for neutron shell closure at N = 308. Ref. 5 also shows a predicted isotope at Uho 500, which is probably an artifact. What Ref. 5 can’t do is describe heavy isotopes of Uho. It is possible to use a first-order, liquid-drop approach to guess at what lies there. At least two computations of the neutron dripline’s location up to Z = 175 exist(6),(7), and since they give similar results, the maximum possible size of a Uho nucleus can be set slightly above the values computed, allowing only a small margin for error. This gives Uho 601 as the heaviest possible Uho isotope. Similarly, a realistic lower bound can be set by requiring that the amount of energy needed to stabilize a nucleus be no more than twice what is needed to stabilize Usp 471. Within this range, the liquid-drop model can be used to indicate the amount of structural correction energy needed to allow a drop of nuclear matter to survive for the 10^-14 sec needed for electromagnetic interactions (such as binding an electron) to become important. Structural correction required for Uho 601 itself is around 1 MeV, which means all Uho drops will fission quickly without structural stabilization. In general, it is not possible to describe structural correction energy. What can be predicted are neutron and proton shell closures, for which correction energy is expected to be particularly large. Neutron shell closures have been predicted at N = 406(7),(8), 370(7), 318(9), and 308(5). The isotope Uho 574 requires a little less than 1.5 MeV of structural correction, which means isotopes in the Uho 564 to Uho 579 band are likely. (See “Formation” for additional significance of these nuclei.) Uho 538 requires around 1.5 MeV of structural correction, which means isotopes in the band Uho 528 to Uho 543 are also likely. All isotopes in both bands should beta-decay with half-lives under a second. On the other hand, Uho 486 requires around 3 MeV of correction energy, which means it is likely to stabilize some nuclei in its vicinity. Ref. 5 does not show a pattern of nuclides which indicate a shell closure at N = 318. Uho 476 requires 4 MeV of correction energy, which is realistic for a strong neutron shell closure, such as the one predicted at N = 308, so the liquid-drop picture isn’t unrealistic. Formation Ions of this element may form when material from roughly 1 km depth is ejected from a disintegrating neutron star during a merger. There is a possibility that beta decay from dripline nuclides stabilized by the N = 406 closure, enhanced by the Z = 164 proton shell closure, will allow some isotopes in the vicinity of Uho 563 to Uho 577 to form in quantity during such a merger. It improbable that nuclides between Uho 528 and Uho 543, or lighter, can form in this way. Fusion or multinucleon transfer reactions in the polar jets emanating from a neutron star or black hole might produce lighter isotopes, including those in the Uho 457 to Uho 484 band. Quantities produced by this method are very small. REFERENCES 5. "Decay Modes and a Limit of Existence of Nuclei"; H. Koura; 4th Int. Conf. on the Chemistry and Physics of Transactinide Elements; Sept. 2011. 6. "Neutron and Proton Drip Lines Using the Modified Bethe-Weizsacker Mass Formula; D.N. Basu et al; Int.J.Mod.Phys.; arXiv:nucl-th/0306061; url: https://arxiv.org/abs/nucl-th/0306061 7. “Single Particle Levels of Spherical Nuclei in the Superheavy and Extremely Superheavy Mass Region”; H. Koura and S. Chiba; Journal of the Physical Society of Japan; DOI 10.7566/JPSJ.82.014201; Jan. 2013. 8. "Magic Numbers of Ultraheavy Nuclei"; V. Yu Denisov; Physics of Atomic Nuclei, v. 68, no. 7, pp 1133-1137; 2005. 9. “The Highest Limiting Z in the Extended Periodic Table”; Y.K. Gambhir, A. Bhagwat, and M. Gupta; Journal of Physics G: Nuclear and Particle Physics. 42 (12): 125105. DOI:10.1088/0954 3899/42/12/ 125105. (12-12-19) References Category:Undiscovered elements Category:Noble gases Category:Radioactive Category:Elements with the melting point of butter. Category:Elements with the melting point of chocolate.